As a solid-state imaging device, a flat light receiving device is being widely used in which photoelectric conversion portions are two-dimensionally arranged in a semiconductor to form pixels, and a signal generated by a photoelectric conversion in each pixel is charge-transferred and read by a CCD circuit or a CMOS circuit. A thing which a photodiode portion using a PN junction is formed in a semiconductor such as Si is generally used as a conventional photoelectric conversion portion.
Recently, as the number of pixels is increased, a pixel size is reduced, and an area of a photodiode portion is reduced, raising a problem that an aperture ratio and light focusing efficiency are reduced, and as a result, the sensitivity is reduced. A solid-state imaging device having an organic photoelectric conversion film using an organic material is being examined as a method of improving an aperture ratio and the like.
A photoelectric conversion device using an organic compound and a solid-state imaging device using the photoelectric conversion device as a light receiving portion are developed. There is disclosed an organic photoelectric conversion device having a structure where a photoelectric conversion layer absorbing light to generate electric charges, and an electric charge blocking layer suppressing injection of electric charges from an electrode are stacked (Patent Document 1). The electron blocking layer having a function of suppressing injection of electrons from the electrode has electron affinity that is lower than a work function of the adjacent electrode by 1.3 eV or more, thereby suppressing injection of the electrons. In the related art, the ionization potential of the electron blocking layer is generally designed to be lower than the ionization potential of the photoelectric conversion layer adjacent thereto in order to efficiently extract a photocurrent. Patent Document 3 discloses a photoelectric conversion device where an ionization potential of an electron blocking layer is higher than the ionization potential of a photoelectric conversion layer adjacent thereto, but a dark current value is not sufficiently low, and sufficient S/N is not obtained. Further, Patent Document 3 does not disclose that the ionization potential of the photoelectric conversion layer is from 5.2 eV to 5.6 eV.
Further, in Patent Document 2, a layer where a p-type organic semiconductor and an n-type organic semiconductor are mixed is used as a photoelectric conversion layer (bulk hetero layer) in order to increase photoelectric conversion efficiency.